Conventional solar energy systems first use a photovoltaic module to acquire DC electricity and then use a DC to DC converter to convert and modulate the acquired DC electricity before using a DC to AC converter, which is structured with bridge rectifying switches, to convert the DC electricity into AC electricity. Finally, this AC electricity is outputted after a LC filter filters out the high frequency part. Because of the nonlinearity between voltage and current of the photovoltaic module, a varied input voltage and current condition will affect the output power of the DC to AC converter.
Particularly, the frequently changing of the intensity of sunlight will cause the great variations of the input voltage and load level of the converter. A weaker intensity of sunlight causes the lighter load and lower conversion rate for the converter. However, no matter if the load of the converter is heavy or light; the control circuit within the converter will consume a substantially constant quantity of energy during operation. Therefore, the percentage of the input energy occupied by the energy consumption of the control circuit will become greater during the light load. Moreover, no matter if the load of the converter is heavy or light, the core loss caused by energy storage inductors and the switching power loss may easily occur on the AC electricity outputted by the converter turning on/off the switching components. Therefore, the conversion rate of the converter becomes inferior under light load.